1. Field of the Invention
The present invention is concerned with an additional attachment for key operated machines.
2. Description of the Prior Art
There exists a broad range of applications for key boards such as the generally wide spread use of the normal keyboard of typewriters and of accounting machines or, however, in the graphic field of the keyboards of photo typesetting machines, linotype machines or the keyboards of correction equipment or display units with a screen which are equipped with further keys for special symbols in addition to the normal keyboard.
These pieces of equipment have in common that letters, numbers, characters or other symbols should visibly be generated using the keyboard by means of various methods or that it should at least be possible to store the letters, numbers, characters or other symbols for further use. Often it is necessary to be able to generate characters with the same piece of equipment which deviate from the characters which are shown on the keys in order to be able for instance, to put in another language such as for instance Greek or Cyrillic or mathematic symbols or even music notes. It can be necessary for the type setting of a photo typesetting machine that a text must be typeset in several languages or in the middle of a normal typesetting word, lines appear in a foreign language which necessitates a corresponding adaptation of the keyboard. This results in a situation that appropriate additional key boards or complete machines of a different type with another keyboard must be available.
One of the most simple additional attachments for the changing of the keyboard covers consists in the pushing or capping respectively of appropriately different marked caps over the individual keys. Furthermore, there are also known so called "flexible covers" which consist of a frame which encompasses the group of keys over which frame a thin flexible membrane is stretched on which membrane pictures of the new symbols are attached in alignment with the keys which are located below these symbols (DF-AS No. 2532762, DT-GM No. 7105085, U.S. Pat. No. 2625330).
These flexible cover areas have the disadvantage that it is almost impossible to prevent an unintended pushing of an adjacent key that was not desired or the unintended pushing of a key can only be prevented if the operator observes the keyboard with a lot of care. In this way there results another disadvantage which is that the skilled operator is not able to write without looking at the original since he cannot feel the contours of the individual keys to which he is used to and therefore he does not know where his fingers are located. Therefore, he is forced to pay a great deal of attention to the keyboard in addition to the text which should be transcribed.
Furthermore, keyboard colors are known which consist of a solid lattice frame which surrounds the individual keys, where each individual row of keys is colored with a flexible tape (DT-PS No. 1277873, DT-PS No. 1955583). Here again the result is that the operator does not have sufficient finger contact with the actual keyboard. Furthermore, the flexible material results in a momentum of forces which must be overcome in addition to the missing keys which is fatiguing for the operator in the long run.